Access text file on client's computer with javacript

I would like my web application to obtain the contents of a .txt file sitting on the desktop of the client. The client will click a menu button (I am using an exotic UI library) and a file dialog will obtain the file path of the .txt as a string. Lets say
myFilePath = "C:\Users\Tom\Desktop\myFile.txt";

With this information in hand, I would then like the contents of this text file to be stored in the string 'myFileContent'.

I understand this is likely to make my browser explode with warnings. Web pages accessing files on your computer... madness. If this is only possible using some other technique, please explain that technique.